Updating backport workflow to include custom branch name (opensearch-project#173)

Signed-off-by: Vacha Shah <vachshah@amazon.com>

Author: VachaShah

.github/workflows/backport.yml

@@ -1,16 +1,20 @@
 name: Backport
 on:
-  pull_request:
+  pull_request_target:
     types:
       - closed
       - labeled
 
 jobs:
   backport:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
     name: Backport
     steps:
       - name: Backport
-        uses: tibdex/backport@v1
+        uses: VachaShah/backport@v1.1.4
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          branch_name: backport/backport-${{ github.event.number }}